Condensed Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Net sales	$ 1,348,661	$ 1,176,470	$ 2,586,771	$ 2,206,854
Cost of goods sold	1,113,777	952,375	2,130,421	1,797,661
Gross profit	234,884	224,095	456,350	409,193
Selling, general and administrative expenses	94,394	100,624	191,773	190,487
Rationalization charges	354	1,942	10,711	4,741
Other pension and postretirement income	(12,818)	(9,705)	(25,637)	(19,410)
Income before interest and income taxes	152,954	131,234	279,503	233,375
Interest and other debt expense before loss on early extinguishment of debt	26,406	25,837	52,829	49,326
Loss on early extinguishment of debt	0	0	883	1,481
Interest and other debt expense	26,406	25,837	53,712	50,807
Income before income taxes	126,548	105,397	225,791	182,568
Provision for income taxes	32,072	27,225	58,034	46,796
Net income	$ 94,476	$ 78,172	$ 167,757	$ 135,772
Earnings per share
Basic net income per share (usd per share)	$ 0.86	$ 0.70	$ 1.52	$ 1.22
Diluted net income per share (usd per share)	$ 0.85	$ 0.70	$ 1.51	$ 1.22
Weighted average number of shares
Basic (in shares)	110,442	110,901	110,323	110,879
Effect of dilutive securities (in shares)	661	433	743	501
Diluted (in shares)	111,103	111,334	111,066	111,380